The present invention relates to multicomponent fibers comprising a thermoplastic polymer surrounding and protecting a starch rich core. The fibers can be used to make nonwoven webs and disposable articles.
There has not been much success at making starch containing fibers on a high speed, industrial level due to many factors. Because of the costs, the difficulty in processing, and end-use properties there has been little or no commercial success. Starch fibers are much more difficult to produce than films, blow-molded articles, and injection-molded articles containing starch. This is because of the short processing time required for starch processing due to rapid crystallization or other structure formation characteristics of starch. The local strain rate and shear rate is much greater in fiber production than other processes. Additionally, a homogeneous composition is required for fiber spinning. For spinning fine fibers, small defects, slight inconsistencies, or non-homogeneity in the melt are not acceptable for a commercially viable process. Therefore, the selection of materials, configuration of the fibers, and processing conditions are critical. In addition to the difficulty during processing, the end-use properties are not suitable for many commercial applications. This is because the starch fibers typically have low tensile strength, are sticky, and are not well suited for fiber-to-fiber bonding in nonwoven webs or substrates.
To produce fibers that have more acceptable processability and end-use properties, it is desirable to use non-starch, thermoplastic polymers in combination with starch. The melting temperature of the thermoplastic polymer should be high enough for end-use stability, to prevent melting or undue structural deformation during use, but low enough so that the starch/thermoplastic fibers can are processable without burning the starch.
There exists today an unmet need for cost-effective, easily processable, and functional starch-containing fibers. The present invention can provide bicomponent fibers that are cost-effective, easily processable, and highly functional. The fibers are made of a starch rich component which is completely surrounded by a thermoplastic polymer component. The starch and polymer bicomponent fiber is suitable for use in commercially available equipment for making bicomponent fibers. There is also a need for disposable, nonwoven articles made from these fibers. The present invention provides such disposable, nonwoven articles made from starch-containing bicomponent fibers.
The present invention is directed to bicomponent fibers. The bicomponent fibers will comprise one component comprising thermoplastic starch which is completely surrounded by and protected by another component comprising a thermoplastic polymer. The configuration of the bicomponent fibers can be sheath-core including, for example, sheath-core with a single core surrounded by the sheath, or a plurality of two or more cores surrounded by a sheath, referred to herein as an islands-in-the-sea configuration.
The thermoplastic polymer protects the starch component. This is particularly relevant during end-use where the starch component alone may not tolerate the environmental conditions without significant loss in fiber properties. The protection may be mechanical, thermodynamic, electrical, solvent based, or combinations thereof. The protection of the starch component also makes the fibers more functional as the fibers are more temperature stable, more resistant to solvents, and able to be thermally bonded.
The present invention is also directed to nonwoven webs and disposable articles comprising the bicomponent fibers. The nonwoven webs may also contain other synthetic or natural fibers blended with the fibers of the present invention. The nonwoven webs may also contain other synthetic or natural fibers blended with the fibers of the present invention. Optional fibers include, but are not limited to, fibers comprising cellulosic pulp, regenerated cellulose, polypropylene, polyethylene terephthalate, and nylon, their various polymers and combinations thereof